I can't get any universal cable to push power into a TE's tesseract anymore.
Cables happily feed RF-based machines, RF-based cables, and tesseracts happily push power into universal cables.
I'm using a bufferless version of EIO's transceivers and they suffer the same issue now.
I have tried to tie up a universal cable to a TE's resonant fluxduct and it works.
Same thing but using a cryo-stabilized fluxduct instead (so no internal buffer), power won't go through.
It seems (but I may be wrong) that univ cables can't push into RF things that have no buffer.

You're quite right, this should now be fixed in development and should be in stable builds soon.